Smoke sensing circuit with battery standby

ABSTRACT

A fire and gas alarm system utilizing a four-terminal sensing device positioned in the environmental region to be monitored. The sensing device includes a pair of resistance heating wires spaced apart by a conducting core and encompassed by an outer metallic shell. A transformer powers a pair of rectifiers which supply current to both a normally operated standby relay and the four-terminal smoke and gas sensing device. When hydrocarbon vapors or smoke impinges upon the metallic shell of the sensing device, the resistance between the pair of heater wires drops to operate a relay and produce an alarm indication. Upon failure of a.c. power, the standby relay is released to connect battery power to the circuit and insure continued operation in response to an alarm condition.

United States Patent [1 1 Caillouet, Jr.

[ 11 3,750,123 July 31, 1973 SMOKE SENSING CIRCUIT WITH BATTERY PrimaryExaminer-John W. Caldwell STANDBY Assistant Ex aminerDaniel Myer [75]inventor: Louis A. Caillouet, Jr., Irving, Tex. Attorney -c l hards,Jerry W. Mills et al.

[73] Assignee: T. J. Connelly Construction Company, Inc., Dallas, Tex.[57] ABSTRACT A fire and gas alann system utilizing a four-terminal [221Flled' 1971 sensing device positioned in the environmental region [21]Appl. No.: 194,679 to be monitored. The sensing device includes a pairof resistance heating wires spaced apart by a conducting core andencompassed by an outer metallic shell. A 2% g 340/237 340/ 6 1 2633transformer powers a pair of rectifiers which supply d 409 current toboth a normally operated standby relay and l 1 /232 E 2 E 5 2 thefour-terminal smoke and gas sensing device. When hydrocarbon vapors orsmoke impinges upon the metallic shell of the sensing device, theresistance between [56] References cued the pair of heater wires dropsto operate a relay and t UNTED STATES PATENTS produce an alarmindicatiom Upon failure of a.c. 3,479,257 11/1969 Shaver 340/237 Rpower, the standby relay is released to connect battery 3,609,732 9/1971Kasahal'a 340/237 R power to the circuit and insure continued operationin 3 1 3 response to an alarm condition. 3 Claims, 2 Drawing Figures 1220 I3 23 24 22 5= M H 50-AC i 1 57 56 1:55

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SMOKE SENSING CIRCUIT WITH BATTERY STANDBY BACKGROUND OF THEINVENTION 1. Field of the Invention This invention relates to alarmsystems and, more particularly, relates to fire and gas alarm systems.

2. History of the Prior Art A wide variety of fire alarm systems haveheretofore been devised. Certain of such prior systems have includeddevices for detecting the presence of smoke or gas in order to actuatealarms, such as a light or a noise source. However, many of thepreviously developed alarm systems have not provided a sufficientlyeconomical and reliable alarm function. Moreover, previously developedfire and smoke alarm systems have not been completely satisfactory inthat they rely exclusively on either commercial a.c. power or uponself-contained battery power. The a.c. powered devices are inoperativeto detect a fire or gas alarm condition in the event of commercial powerfailure. The battery powered devices-are inherently expensive andsomewhat unreliable because the batteries must be replaced periodicallyto insure continuous operability. The present invention combines thedesirable features of both a.c. and battery power by providing batterypower utilized automatically only in the event of a power failure.

SUMMARY OF THE INVENTION In accordance with the present invention, analarm system is provided which eliminates or tends to reduce theproblems and deficiencies of previously developed systems. The presentalarm system requires a relatively simple dc. power supply and a singlegas or smoke detector. The detector of the present invention is smalland inconspicuous and requires only low voltage so that specialinstallation, structure and techniques-are not required.

In accordance, with the present invention, an alarm system is providedwith includes a detector operable to generate electrical signals inresponse to thepresence of vaporous hydrocarbons. A low voltage powersupply isconnected to energize thedetector, with an electronic switchoperable in response to the electrical signals generated thereby. Analarm device is-operableby the electronic switch to generate analarmindication.

In accordance with a more'specific aspect of the invention,-a fire andgas alarm system includes a fourterminal sensing device adaptedtobepositioned in an environmental region to be monitored. The sensingdevice includes first and'second resistance heating wires spaced apartby a conducting core and encompassed by an outer metallic shell. An a.c.source is rectified to supply a low voltage which is connected to heatthe first resistance "heating wire. The terminals of the second heatingwire are-connected for generationof electrical alarm signals upon theimpingement of hydrocarbon vapors upon the outer metallic shell. Astandbybattery relay is operated from the a.c. power andprovidescurrentto the resistance heating wire in the event of power failure. An alarmstructure is operable in response to the electrical alarm signals forgeneratingalarm indications with or without a.c. power.

DESCRIPTION OF THE DRAWlNG For a more complete understanding: of thepresent invention and 'for further objects and advantages thereof,reference is now made to the following description taken in conjunctionwith the accompanying drawing, in which:

FIG. 1 is a schematic diagram of the preferred embodiment system; and

FIG. 2 is a somewhat diagrammatic illustration of a sensor constructedin accordance with the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. 1, a powerplug 10 is adapted to be plugged into a 220 volt, 50 H a.c. poweroutlet. The present embodiment of the invention is especially intendedfor operation with the conventional commercial power most commonly foundin European countries. The plug 10 is connected across the primarywinding 11 of a power transformer 12. A dropping resistor 13 and a neonindicator lamp 14 are connected in series across the primary transformerwinding 11 to provide a visual indication of whether or not the a.c.power source is operating. The transformer 12 also includes first andsecond secondary winding 15 and 16, respectively. The turns ratio of theprimary winding 11 to the first secondary winding 15 is designed toproduce an output on the order of 1 volt and deliver current on theorder of 500 milliamperes. The winding 15 is connected across a firstheating filament 21 of a smoke and hydrocarbon gas sensing unit 20 to bedescribed in further detail below.

The second secondary winding 16 is connected in series with a pair ofdiodes 31 and 32 forming a first halfwave rectifier 17. The output ofthe diodes 31 and 32 is connected across a capacitor 33 and a resistor34 which together form a ripple filter for the rectifier. A droppingresistor 35 is connected across the output of the 'RC filter formed bycapacitor33 and resistor 34 and to one end of a second heating filament22 of the sensing unit 20.

A second pair of diodes 36 and 37 are also connected across thesecondary winding 16 to form a second halfwave rectifier 18. A capacitor39 is connected across the two diodes 36 and 37 to form a ripple filter.The diode 37 is connected in series with a resistor 3,8.and the winding41 of a standby power relay 40. The standby relay 40 includes a firstand second pair of contacts 42 and 43, respectively, which are both openwhen the relay is operated. One contact 42a of the first set 42is-connected to thecollector electrode'of a transistor through thewinding 45 of an alarm relay 46. The other contact 421: of the set 42 isconnectedto the positiveelectrode of a 6-volt emergency battery 47and-throughan isolation diode 48 to a contact 43aof the other contactset- 43. The negative-electrode of the battery 47 is grounded. Thecontact 43a is also connected to'thenegativ'e electrodeof a -1.5'voltemergency battery 49, the "positive electrode of which is connected.toone'terminal of the second heating filament of the sensing device 20.The contact 43b of the set'43 is connected to the other terminal of thefilam'ent 22. A blocking diode-51 is connected between the secondrectifier and the winding .45 of the relay 46 to isolate the standbyd.c. powerfrom the rectified.a.c.

power.

The alarm relay-46-includes one pair of normally open contacts 52 whichare connected from the'negative terminal of the blocking diode 51 to analarm buzzer 53.

The transistor 44 is connected in the grounded emitter configurationthrough a resistor 54. The base electrode of the transistor 44 isconnected through a base resistor 55 to one side of the secondarytransformer winding 15. A potentiometer 56 has one terminal connected tothe secondary winding with the wiper contact 57 grounded.

FIG. 2 illustrates the partial cutaway view of a typical sensor showingfour terminals 23 26 which extend from a ceramic base 27. A 400-gaugemesh screen 28 provides a cylindrical container which is topped off by asteel cap 29. The mesh screen 28 allows hydrocarbon vapors to penetratewithin the sensor and impinge upon a sensing pod 30 which comprises anouter shell of Corundum, a natural aluminum oxide. Paladium heatingelements are exposed within the Corundum outer shell and are spacedapart by an alpha alumina inner spacer core. Although the operation ofthe sensing pod is not absolutely understood, it is believed that theelectrical heating wires heat the pod up such that the pod generates apredetermined electrical signal from the output terminal thereof. Whenhydrocarbons from smoke or gas strike the Corundum, the resistancebetween the two resistance heating wires decreases to cause theelectrical output of the device to rise to indicate the presence ofhydrocarbon vapors.

Referring again to FIG. 1, when a.c. power is aplied to the terminals ofthe plug 10, the diodes 31 and 36 together with the capacitor 33 and theresistor 34 produce a d.c. potential at point 60 on the order of apositive 6 volts. The output of the secondary winding 15 is connectedacross the terminals 23 and 24 of the sensor 20 to deliver a voltage onthe order of 1 volt to the first heating filament 21. When one of thefilaments of a sensor 20 is heated, the resistance between the filaments21 and 22 is fairly high, for example, on the order of several thousandohms. The voltage at the base of the transistor 44 is normallymaintained at a level below the turn-on potential due to the adjustmentof the wiper arm 57 of the potentiometer 56 and the relatively highresistance between the filaments 21 and 22, the latter being connectedto the positive 6 volt potential at point 60. While the transistor 44 isin a nonconductive state, the alarm relay 46 remains unoperated.

As long as the a.c. power source is operating, the second rectifier 18comprising the diodes 36 and 37 together with the filter capacitor 39produce d.c. current flow through the resistor 38 and the winding 41 ofthe standby relay 40 to hold the relay operated and the contact sets 42and 43 open.

In the event the sensor 20 is subjected to smoke or hydrocarbon vapors,the resistance between the heated filament 21 and the other filament 22falls to a much lower value, for example, less than I00 ohms. Thepositive voltage on the base of the transistor 44 rises to a valuesufficient to initiate conduction through the collector-emitter path andoperate the alarm relay 46 to close the contacts 52 and energize thealarm buzzer 53. Once energized, the buzzer 53 will continue to operateand produce an alarm indication until the smoke or hydrocarbon vaporclears and the resistance between the filaments 21 and 22 rises to stopconduction in the transistor 44.

In the event of an a.c. power failure, the second rectifier l8 comprisedof the diodes 36 and 37 and the capacitor 38 ceases producing a d.c.output voltage to energize the winding 41 and the standby relay 40releases to close the contact sets 42 and 43. Closure of the contacts 42connects the positive terminal of the 6 volt standby battery 47 to thecollector electrode of the transistor 44 through the winding 45 of thealarm relay 46. Closure of contacts 43 connects the 1.5 volt standbybattery 49 across the other filament 22 of the sensor 20 to heat thefilament so that the sensor 20 remains sensitive to detection of smokeor hydrocarbon vapors. The positive 6 volt potential of the standbybattery 47 is also connected through the isolation diode 48 and thecontacts 43 to produce a positive 6 volt potential at the point 60.

Upon exposure of the sensor 20 to smoke or hydrocarbon vapors, theresistance between the two filaments 21 and 22 is reduced so that thetransistor 44 is biased into conduction to operate the alarm relay 46through its emitter-collector path and energize the alarm buzzer 53.

When a.c. power is reestablished, current again flows through the secondrectifier 18 formed by the diodes 36 and 37 to reenergize the coil 41 ofthe standby relay 40 and disconnect the emergency batteries 47 and 49from the circuit. Current is drawn from the batteries 47 and 49 onlyduring a period of a.c. power failure, thereby extending their usefullives.

From the foregoing, it will be understood that the present inventionprovides an alarm system which detects a fire or gas emergency. Thepresent system is relatively simple in construction andmaintenance-free. The gas sensing detector utilized is small and may beoperated with only a low voltage requirement. The system of the presentinvention functions to automatically change from a.c. to standby batteryupon the occurrence of a power failure and again returns to a.c. powerupon reestablishment thereof. The circuit functions in generally thesame manner whether being operated by a.c. power or standby batteries.

Having described the invention in connection with certain specificembodiments thereof, it is to be understood that further modificationsmay now suggest themselves to those skilled in the art and it isintended to cover such modifications as fall within the scope of theappended claims.

What is claimed is:

1. A fire and gas alarm system comprising:

a four-terminal sensing device adapted to be positioned in anenvironmental region to be monitored, said sensing device includingfirst and second resistance heating wires spaced apart by a conductingcore and encompassed by an outer metallic shell, the resistance betweensaid wires being decreased when vaporous hydrocarbons or smoke arepresent in said environmental region;

connection to an a.c. voltage source, said transformer having first andsecond secondary windings, said first secondary winding being connectedto a first of said resistance heating wires of said sensing device toprovide current flow therethrough when a.c. power is supplied to saidtransformer;

pair of rectifiers connected to the second of said transformer secondarywindings, the output of the first rectifier being connected to thesecond of said resistance heating wires of said sensor to provide a biasvoltage thereto;

transformer having a primary winding adapted for a standby power relay,actuated by the output of the second rectifier of said pair and havingnormally open terminals connected to a source of battery power and toone of the resistance heating wires of said sensing unit;

an alarm relay having a set of normally open con-' tacts;

a transistor connected in a common emitter configuration having its baseelectrode coupled to the first of said resistance heating wires and itscollector electrode connected through the winding of said alarm relay tothe output of said second rectifier;

an alarm buzzer connected to contacts of said alarm relay whereby thepresence of smoke or gas within the region of said sensor decreases theresistance between the heating wires to produce a voltage at the baseelectrode of said transistor sufficient to bias said transistor intoconduction and actuate said alarm relay to produce an alarm buzzersignal.

2. A fire and gas alarm system comprising:

a four-terminal sensing device adapted to be positioned in anenvironmental region to be monitored, said sensing device includingfirst and second resistance heating wires spaced apart by a conductingcore and encompassed by an outer metallic shell, the resistance betweenat least one of said wires being decreased when vaporous hydrocarbons orsmoke are present in said environmental region;

a transformer having a primary winding adapted for connection to an a.c.voltage source, said transformer having first and second secondarywindings, said first secondary winding being connected to a first ofsaid resistance heating wires of said sensing device to provide currentflow therethrough when a.c. power is supplied to said transformer;

a pair of rectifiers connected to the second of said transformersecondary windings, the output of the first rectifier being connected tothe second of said resistance heating wires of said sensor to provide abias voltage thereto;

a standby power relay, actuated by the output of the second rectifier ofsaid pair and having normally open terminals connected to a source ofbattery power and to one of the resistance heating wires of said sensingdevice;

an alarm relay having a set of normally open contacts;

transistor switch means having an electrode coupled to the first of saidresistance heating wires and a second electrode coupled through thewinding of said alarm relay to the output of said second rectifier; and

an alarm connected to contacts of said alarm relay whereby the presenceof smoke or gas within the region of said sensor decreases theresistance between the heating wires to produce a voltage at saidtransistor switch means sufficient to bias said transistor intoconduction and actuate said alarm relay to produce an alarm signal.

3. A fire and gas alarm system comprising:

a four-terminal sensing device adapted to be positioned in anenvironmental region to be monitored, said sensing device includingfirst and second resistance heating wires spaced apart by a conductingcore and encompassed by an outer shell, the resistance between at leastone of said wires being decreased when vaporous hydrocarbons or smokeare present in said environmental region;

a transformer having a primary winding adapted for connection to an a.c.voltage source, said transformer having first and second secondarywindings, said secondary winding being connected to a first of saidresistance heating wires of said sensing device to provide current flowtherethrough when a.c. power is supplied to said transformer;

rectifier circuitry connected to the second of said transformersecondary windings and to the second of said resistance heating wires ofsaid sensor to provide a bias voltage thereto;

a standby power relay connected to said rectifier circuitry and havingnormally open terminals connected to a source of battery power and toone of the resistance heating wires of said sensing device;

an alarm relay having a set of normally open contacts;

a transistor connected in a common emitter configuration having its baseelectrode coupled to the first of said resistance heating wires and itscollector electrode connected through the winding of said alarm relay tothe output of said rectifier circuitry; and i an alarm connected tocontacts of said alarm relay whereby the presence of smoke or gas withinthe region of said sensor decreases the resistance between the heatingwires to produce a voltage at the base electrode of saidtransistorsufficient to bias said transistor into conduction and actuatesaid alarm relay to produce an alarm signal.

t ll

1. A fire and gas alarm system comprising: a four-terminal sensingdevice adapted to be positioned in an environmental region to bemonitored, said sensing device including first and second resistanceheating wires spaced apart by a conducting core and encompassed by anouter metallic shell, the resistance between said wires being decreasedwhen vaporous hydrocarbons or smoke are present in said environmentalregion; a transformer having a primary winding adapted for connection toan a.c. voltage source, said transformer having first and secondsecondary windings, said first secondary winding being connected to afirst of said resistance heating wires of said sensing device to providecurrent flow therethrough when a.c. power is supplied to saidtransformer; a pair of rectifiers connected to the second of saidtransformer secondary windings, the output of the first rectifier beingconnected to the second of said resistance heating wires of said sensorto provide a bias voltage thereto; a standby power relay, actuated bythe output of the second rectifier of said pair and having normally openterminals connected to a source of battery power and to one of theresistance heating wires of said sensing unit; an alarm relay having aset of normally open contacts; a transistor connected in a commonemitter configuration having its base electrode coupled to the first ofsaid resistance heating wires and its collector electrode connectedthrough the winding of said alarm relay to the output of said secondrectifier; an alarm buzzer connected to contacts of said alarm relaywhereby the presence of smoke or gas within the region of said sensordecreases the resistance between the heating wires to produce a voltageat the base electrode of said transistor sufficient to bias saidtransistor into conduction and actuate said alarm relay to produce analarm buzzer signal.
 2. A fire and gas alarm system comprising: afour-terminal sensing device adapted to be positioned in anenvironmental region to be monitored, said sensing device includingfirst and second resistance heating wires spaced apart by a conductingcore and encompassed by an outer metallic shell, the resistance betweenat least one of said wires being decreased when vaporous hydrocarbons orsmoke Are present in said environmental region; a transformer having aprimary winding adapted for connection to an a.c. voltage source, saidtransformer having first and second secondary windings, said firstsecondary winding being connected to a first of said resistance heatingwires of said sensing device to provide current flow therethrough whena.c. power is supplied to said transformer; a pair of rectifiersconnected to the second of said transformer secondary windings, theoutput of the first rectifier being connected to the second of saidresistance heating wires of said sensor to provide a bias voltagethereto; a standby power relay, actuated by the output of the secondrectifier of said pair and having normally open terminals connected to asource of battery power and to one of the resistance heating wires ofsaid sensing device; an alarm relay having a set of normally opencontacts; transistor switch means having an electrode coupled to thefirst of said resistance heating wires and a second electrode coupledthrough the winding of said alarm relay to the output of said secondrectifier; and an alarm connected to contacts of said alarm relaywhereby the presence of smoke or gas within the region of said sensordecreases the resistance between the heating wires to produce a voltageat said transistor switch means sufficient to bias said transistor intoconduction and actuate said alarm relay to produce an alarm signal.
 3. Afire and gas alarm system comprising: a four-terminal sensing deviceadapted to be positioned in an environmental region to be monitored,said sensing device including first and second resistance heating wiresspaced apart by a conducting core and encompassed by an outer shell, theresistance between at least one of said wires being decreased whenvaporous hydrocarbons or smoke are present in said environmental region;a transformer having a primary winding adapted for connection to an a.c.voltage source, said transformer having first and second secondarywindings, said secondary winding being connected to a first of saidresistance heating wires of said sensing device to provide current flowtherethrough when a.c. power is supplied to said transformer; rectifiercircuitry connected to the second of said transformer secondary windingsand to the second of said resistance heating wires of said sensor toprovide a bias voltage thereto; a standby power relay connected to saidrectifier circuitry and having normally open terminals connected to asource of battery power and to one of the resistance heating wires ofsaid sensing device; an alarm relay having a set of normally opencontacts; a transistor connected in a common emitter configurationhaving its base electrode coupled to the first of said resistanceheating wires and its collector electrode connected through the windingof said alarm relay to the output of said rectifier circuitry; and analarm connected to contacts of said alarm relay whereby the presence ofsmoke or gas within the region of said sensor decreases the resistancebetween the heating wires to produce a voltage at the base electrode ofsaid transistor sufficient to bias said transistor into conduction andactuate said alarm relay to produce an alarm signal.